There was a time when only four types of headlights were permitted in the US: two big round, four small round, two big rectangles, or four small rectangles – all standard sealed beam units, all horrible for visibility. Jaguar had the gall and audacity to design their saloon of the day to utilize two large round and two small round, found out that wasn’t permitted, and ended up replacing the large round units with small round units with an ugly spacer surrounding it.
In the midst of the “energy crisis”, the Big Three auto makers made a case to Congress that they could improve their corporate fuel economy if they were permitted to utilize custom headlight assemblies that would fit the contours of the car smoothly. The laws were subsequently changed permitting pretty much whatever headlights the automakers wanted provided they garnered DOT approval – meaning, basically, they still had to suck for visibility. This introduced the 9000 series bulbs, one of which looked a lot like a European H4 except that it was DOT-approved.
Nowadays we have LED headlights and pretty much anything goes. Which means you can pitch your old four-round sealed beam arrangement over the hedge and replace it with something that actually enables you to see at night if you so choose. DOT approval is still required, but unless you blind an oncoming cop you’re not likely to get called on it.